ZERO is now well nothing....

In a trading card game long long ago zero was always considered to be a legal number. So you could shuffle zero cards into your deck if your hand had zero cards.

But things seem to be changing...

== FAST BALL (Skyridge)

Q. When using Fast Ball, if the very first card you turn up is an
evolution, do you still have to shuffle your deck?
A. If FastBall pulls an Evolution Card as the first revealed card, the
deck is not shuffled as there are no as there are no "other revealed
cards" to shuffle back in. (Jan 15, 2004 PUI Rules Team)

well before you would still shuffle the deck but not any longer .

so what now with similar game effects? Like Copycat. With zero cards to shuffle in do we no longer shuffle when in the past we would? Or worse with no cards to shuffle are we now unable to even play the card? There are some rullings that indicate that if you can't do everything then you get to do nothing.

We actually had a long discussion about this ruling and initially a lot of us were thinking that you would shuffle your deck.
However, it came down to comparing the rulings on Prof. Elm and the rulings on Lass.

Prof Elm says to shuffle your hand in, which is a Zone. The Zone always exists and so you would always shuffle since the "Hand" always exists.

The Lass rulings was that if there were no Trainers revealed, then there were no Trainers to shuffle into your deck and therefore you didn't shuffle. There was no "Zone" of "Trainer cards.

Fast Ball was similar to Lass. You shuffled "other revealed cards" into your deck. If there are no "other revealed cards", there is nothing to shuffle and so you don't shuffle.

It's not a change like the Energy Search ruling.
THAT is a big change.

Q. For Lass, does the player have to shuffle their deck if there are no trainers in their hand?
A. No. You [only] have to shuffle when you put cards back into your deck. (Nov 30, 2000 WotC Chat, Q4 & Q15)